In the field of engine-generators, it is common to utilize an electronic control module for sensing a variety of parameters and responsively controlling a plurality of electric actuators, such as coils in response to the sensed parameters. However, in such prior systems, it is possible for the coils to be inadvertently energized if electrical leads from the control module are connected incorrectly to a power source.
This problem can be better understood by referring to FIG. 1. FIG. 1 illustrates a driver circuit 10 for controlling a plurality coils 12. Two coils 12a,12b are shown for illustration purposes; however, the driver circuit can be used for any number of coils. The drive circuit 10 is part of an electronic control module (not shown). The control module forms no part of the subject invention and, therefore, it will not be described in detail. The driver circuit 10 includes first and second control switches 14a,14b, each being coupled in series between a first terminal 16a-16b of a respective coil 12a-12b and a first common junction 18. The first common junction 18 is normally connected to a positive reference terminal 20 of an electrical power source 22, such as a battery, by a first electrical conductor 21. The control switches 14a,14b are adapted to controllably connect the solenoid first terminals 16a-16b to the power source positive reference terminal 20 in response to control signals supplied by the control module, as is explained below. The control switches are commonly in the form of relays; however, numerous other switches such as bipolar or MOSFET transistors, could also be used.
The coils 12a,12b further have respective second terminals 24a-24b which are connected at a second common junction 26. The second common junction 26 is normally connected to a negative reference terminal 28 of the power source 22 by a second electrical conductor 30. First and second flyback diodes 32a,32b provide respective current flyback paths for the first and second coils 12a,12b during deenergization. The flyback diodes 32a,32b, also prevent arcing across the control switches 12a,12b during deenergization of the coils 12a,12b. More specifically, each flyback diode 32a,32b has a cathode connected to a respective coil first terminal 16a,16b and an anode connected to a third common junction 34. The third common junction 34 is normally connected to the power source negative reference terminal 28 by a third electrical conductor 36.
Operation of the driver circuit will now be briefly described using an example. In the case of a normally-closed switch, such as the second switch 14b, the associated coil 12b is normally energized. If a condition is sensed, wherein it is desirable to deenergize the second coil 12b, the control module controllably opens the second control switch 14b. When this occurs, the second coil 12b is electrically disconnected from the power source positive reference terminal 20 and energy stored in the second coil 12b must be dissipated. The stored energy dissipates as current from the coil 12b circulates through the second flyback diode 32b. Operation of a normally open switch, such as first control switch 14a, is similar and will not be further described.
At least two undesirable conditions can occur, however, if the driver circuit 10 is incorrectly connected to the power source 22, as is illustrated in FIG. 1b. In FIG. 1b, the first and third common junctions 18,34 are connected to the negative and positive power source reference terminals 20,28. This type of connection will hereinafter be referred to as a reverse-polarity battery connection, and a connection as shown in FIG. 1a will hereinafter be referred to as a normal battery connection.
The first undesirable condition can occur in a normally open switch, such as the first control switch 14a. In this instance, the first coil 12a will be energized by the current path through the first flyback diode 32a. The severity of this type of fault depends on what the first coil 12a is used for. For example, if the first coil 12a is used to control a starting motor (not shown) on the engine, the engine may accidentally start. The second undesirable condition occurs in the case of a normally closed switch, such as the second control switch 14b. In this instance, a high level current will flow through the second control switch 14b. Fuses 38a,38b are typically connected between the control switches 14a,14b and the power source positive reference terminal 20 to prevent damage to the control switches 14a,14b in such an instance. The fuses 38a,38b are designed to fail before the current reaches a level that can damage the control switches 14a,14b. However, it is also possible for the diode 32b associated with the closed control switch 14b to fail during a reverse-polarity battery connection. In either instance, the control module is disabled, and the resulting loss in operation, as well as the cost of repairing the failed components make this an undesirable condition.
These problems could be avoided by using a harness-type connector to prevent a reverse-polarity battery connection. However, the generator market dictates that individual post-type connectors be provided on the control module. The above problems could also be solved by connecting the coil second terminals 24a,24b directly to the third common junction 34 and using single electrical conductor to connect the third common junction 34 to the power source positive reference terminal 28. However, the driver circuit 10 isn't typically in close proximity to the coils 12a,12b and, therefore, this type of connection is not readily attainable.
The present invention is directed to overcoming one or more of the problems as set forth above.